The present invention relates to a towing and towed vehicle braking system, and in particular, to a towing and towed vehicle braking system that utilizes a proportional relief valve to apply a braking force to the towed vehicle brakes in response to a signal from the towing vehicles braking system
The number of vehicles on the roadways towing trailers and other vehicles continues to increase, especially with the proliferation of sport utility vehicles. In any towing and towed vehicle combination, the vehicles must stop and start together. For these reasons state and federal regulations require that towed vehicles over a certain gross vehicle weight (GVW) provide brakes on the towed vehicle. Regulatory schemes vary such that some regulations require trailer brakes for trailers with a GVW of 1,000 pounds and above. Federal law provides not only for the inclusion of brakes on towed vehicles, but also that the operator of the towing vehicle controls the towed vehicle""s brakes. In addition, the towed vehicle must include some mechanism to activate the towed vehicle brakes in the event that the towed vehicle breaks away from the towing vehicle.
To meet these demands manufactures of towed vehicle braking systems use a variety of types of brake systems. Hydraulic surge-brakes comprise one such type. Typically surge brakes use mechanical devices to actuate a brake cylinder, usually a master brake cylinder, in response to inertial pressure differential between the towing vehicle and the towed vehicle that develops upon deceleration of the vehicles. The simplicity of surge brakes, however, often leads to drawbacks. The brakes generally lack the ability to adjust braking force in response to changes in trailer loads, and lack the ability to vary braking force in proportion to the braking force applied by the operator of the towing vehicle. These drawbacks can result in the towed vehicle stopping faster than the towing vehicle in which case the towed vehicle drags the towing vehicle, or the opposite can result whereby the towing vehicle stops faster than the towed vehicle causing the towed vehicle to push the towing vehicle. In either case,.the condition can substantially impair the ability of the operator to maintain control. Furthermore, in many cases conventional surge brakes no longer meet the stricter federal guidelines.
Other types of brakes used with towing vehicles include electrical brakes, electric over hydraulic, vacuum over hydraulic, and air over hydraulic. However, in addition to the drawbacks mentioned in connection with surge brakes, these other systems each suffer from substantial drawbacks. For instance, electric brakes use an electromagnet working against a disc, and through mechanical leverage apply drum brakes. Electric brakes are troublesome by nature, have slow response times, and tend to be high maintenance, especially, for towing vehicles like boat trailers that encounter water, particularly salt water. In addition, the vacuum over hydraulic and air over hydraulic braking systems are extremely expensive.
In recent years hydraulic surge braking systems have undergone some improvement. In particular, U.S. Pat. No. 5,779,324 (Cords et al.) discloses a surge brake that includes a switching control box that allows the operator of the towing vehicle to select between three different braking forces. The switching control box activates one of three pressure control check valves to vary the braking force. However, the braking force is not proportionally adjustable in real-time, but instead requires manual operator intervention to vary the braking force applied to the towed vehicle.
U.S. Pat. No. 6,296,323 (Cords) discloses a complicated hydraulic brake system that utilizes a continuously variable hydraulic pressure means to provide a proportional braking force. The system relies on a variation in pressure drop, across an fixed orifice valve produced in response to variations in electrical motor speed, to vary the volume of fluid delivered to the towed vehicle braking system. However, the design of the system produces heat causing instability because as the temperature of the fluid increases viscosity drops changing the properties of the pressure drop across the orifice. Heat changes the viscosity of the brake fluid, which in turn changes the amount of braking force required to maintain a given brake-line pressure. In other words, the pressure drop across the fixed orifice creates a certain amount of heat. This heat lowers the viscosity of the brake fluid, which reduces the pressure in the brake lines at a given volume. This, in turn, requires the system to increase the pressure across the orifice, which adds more heat. Accordingly, the heat inducing nature of the system actually works against itself in its attempt to control brake pressure, thereby requiring constant adjustments.
Accordingly, a need exists for an improved towed vehicle braking system that provides for application of a proportionally variable braking force to the brakes of a towed vehicle without the drawbacks and complications of prior art systems.
An object of the present invention comprises providing an improved towing and towed vehicle braking system.
These and other objects of the present invention will become apparent to those skilled in the art upon reference to the following specification, drawings, and claims.
The present invention intends to overcome the difficulties encountered heretofore. To that end, a towing and towed vehicle braking system is provided comprised of the following components. A towing vehicle having brakes in operable communication with a towing vehicle electronic brake controller capable of transmitting a brake signal indicating application of the towing vehicles brakes. A towed vehicle coupled to the towing vehicle having brakes in operable communication with a towed vehicle electronic brake controller capable of receiving the brake signal from the towing vehicle electronic brake controller. Brake lines leading to the towed vehicle brakes. A power unit in operable communication with the towed vehicle brake controller and the brakes lines, for providing a power source to pressurize the brake lines. A brake fluid reservoir in operable communication with the power unit and the brake lines, for storage and transfer of brake fluid. A proportional relief valve in operable communication with the power unit, the towed vehicle brake controller, the brake lines, and the brake fluid reservoir, for controlling the pressure in the brake lines and thereby controlling braking force applied by the towed vehicle brakes. Wherein the proportional relief valve is sent a specific pressure setting by the towed vehicle brake controller set in response to the brake signal from the towing vehicle electronic brake controller, thereby controlling the application of the towed vehicle brakes in response to the towing vehicle brakes.